Download supergene enrichment

intro
Saturday, September 11, 2021
2:37 PM
• Insitu enrichment of Cu, Zn, Ag, Au by weathering.
• It’s a product of Oxydation and Hydrolysis of sulphide minerals at
upper part of weathering profile
• Form blanket of 2ndary(supergene) above primary Cu deposit
(Hypogene)
Form low grade porphyry cu deposits
Supergene Oxidation
• Supergene deposit can occur in any environmenet ( unlike
laterituzation requires particular condition)
• GW leach Cu from sulphide material
• Most of the porphyry cu env , dominant phase is Pyrite
Its oxd. And hyd. Produce H+, reduce pH - make Acidic env in
weathering zone.
• Cu2+ dissole in ground water
• Residual - Haematite or goethite + clay and skeletal out line of
original sulphide ( called gossan)
• Leaching solution looses a part of metallic content in zone of oxidation
and form oxide ore
• Some iron are transported as Fe2+ elsewhere,, while remaining form
insitu limonite that occupies void left by sulphide.
• Downward percolating Cu , encounters reducing env and secondary Cu
mineral ppt
secondary Cu mineral comp. depends on- - comp. of GW
- Eh- pH condition
Cu also replaces pre-existing sulfide minerals (i.e. pyrite and
chalcopyrite- Fe- minerals) in more reduced form chalcocite (Cu2S),
covellite (CuS), and bornite (Cu5FeS4)
• The primary, hypogene ore is considered to be hosted in a granite and
comprises pyrite + chalcopyrite that is weathered by a flux of slightly
acidic rainfall
• copper is reprecipitated as chalcocite and covellite by replacement of
pyrite and chalcopyrite
Changes in oxidation zone
1. Formation of sulphuric acid and and iron sulphate
2. ferrous to ferric sulphate (oxd)
ferous oxide form limonite ppt insitu
H2SO4 and ferric sulphate lowers pH , helps in leaching metals
Metals form sulphate and goes into the soln
Deposition in oxidation zone
Sunday, December 12, 2021
7:40 PM
Differential dissolution occurs
Stable min. in gossann stage 1 and 2, - hematite/goethite, alunite, and quartz.
Stage 3 - gibbsite, muscovite/sericite,clay
Stage 4 - sericite and kaolinite
• Chalcopyrite is completely leached before Pyrite (in stage 1)
Only some pyrite remains in stage 2 till stage 3
When alunite and SO42- removed by s3,…pH increases from acidic to
alkaline
Stable mineral in supergene enrichment zone
S1 and s2 - covellite , chalcocite
from s2 , when cpy is consumed Cu flux reduces- Bornite starts ppt